Crystal Palace beat West Ham to pile the pressure on Hammers boss Graham Potter amid fan protests before and during the match at London Stadium.
Jean-Philippe Mateta pounced to nod in the rebound after goalkeeper Alphonse Areola had pushed Marc Guehi's header on to the crossbar as the visitors took a 37th-minute lead.
Jarrod Bowen equalised early in the second half when he pulled away from his marker to head into the net following El Hadji Malick Diouf's corner.
The home fans responded as their side enjoyed a bright spell, but Lucas Paqueta had an effort cleared off the line by Chris Richards, with Kyle Walker-Peters also unable to convert two opportunities.
West Ham's failure to grab a second goal proved costly as Tyrick Mitchell was afforded too much space in the penalty area and controlled a superb volley into the net for what proved to be the winner.
Earlier on Saturday, about 3,000 Hammers fans protested before the match, with angry supporters holding flags and banners and chanting about chairman David Sullivan and vice-chair Karren Brady.
The unhappiness continued during the game as there were more "sack the board" chants from the home supporters when the match was goalless, with the hosts booed off at half-time when they were trailing and again at the final whistle.
West Ham's miserable day continued as Palace fans chanted "you're getting sacked in the morning" at Potter, with some of the home supporters joining in.
Potter has now only won six of his 23 league games and picked up 23 points since replacing Julen Lopetegui in January. The Spaniard also collected 23 points from his spell in charge, but did so in three fewer games.
West Ham analysis: Defensive woes cost Hammers again
Once more, West Ham's failure to defend set-pieces proved crucial. Before the game, six of their 11 goals conceded in the Premier League had been from corners, while no other team had let in more than three.
But the Hammers once more struggled with deliveries into the penalty area. Daichi Kamada gave them an early warning and forced Areola, who replaced Mads Hermansen for his first league start of the season, to tip the ball over.
Guehi, who saw a transfer deadline day move to Liverpool break down after Brighton's Igor Julio went on loan to West Ham instead of Palace, rose superbly to head at goal and Areola was unlucky his excellent save only fell to Mateta.
London Stadium has often been criticised by West Ham fans unhappy the atmosphere is a pale comparison to their previous home Upton Park.
Bowen's goal gave West Ham hope and instantly lifted the mood around the ground, with the hosts on top and the supporters giving them their full backing.
But more defensive problems from the hosts ruined their good work, with Mitchell given far too much time to volley into the roof of the net.
Next up is a match against former boss David Moyes, with the Hammers travelling to Everton on 29 September.
Some West Ham fans wanted Moyes out following a ninth-placed finish two seasons ago, a year after he had guided them to their first major trophy in 43 years.
It is hard to see how the club have progressed in any way since then.
Crystal Palace analysis: Glasner's side hit new heights
While West Ham are a club in turmoil on and off the field, Crystal Palace fans have never had it so good.
This victory takes the Eagles fourth with Oliver Glasner's side still unbeaten after nine games in all competitions this season, more than any other top-flight team.
Despite selling star player Eberechi Eze to Arsenal, Glasner has helped them to two wins and three draws from their opening five matches, as well as winning the Community Shield by beating Premier League champions Liverpool on penalties.
The Eagles have also negotiated their way into the main phase of the Conference League in their first ever European campaign and also defeated south London rivals Millwall to reach the last 16 of the Carabao Cup.
Away fans sung about their FA Cup win in May and their forthcoming European tour - and these are glorious times for the Palace supporters.
What will have particularly pleased Glasner is how his side shut out West Ham after they took the lead for the second time, with the hosts creating no late chances and Palace holding on to their lead with relative ease.
What's next for both sides?
The West Ham fans who were involved in the protest before this match have said they will boycott the next home game against Brentford in a month's time.
Before then, the Hammers play at Everton on Monday, 29 September and at Emirates Stadium against Arsenal on Saturday, 4 October.
Crystal Palace entertain reigning champions Liverpool on Saturday, 21 September in a rematch of this season's Community Shield, which the Eagles won 3-2 on penalties after it had finished 2-2.
After that comes Palace's first-ever game in the main phase of a European competition, when they take on Dynamo Kyiv in the Conference League having won a two-legged qualifying tie against Fredrikstad in August.
